The present invention relates to a sheet material cutting device which cuts a sheet material by the cooperation of a circular rotary cutting blade and a fixed cutting blade formed into a long sheet.
In prior known printers for a terminal such as ECR or POS, a strip-shaped sheet material wound into a roll is pulled out for printing, and then the necessary portion is cut into a sheet for delivery by a cutter.
Various types of such sheet material cutters are available. The rotary-type cutter requires a high manufacturing cost and causes a relatively high degree of noise and therefore is now being replaced by a cutter based on a combination of a circular rotary cutting blade moving while rotating and a fixed cutting blade formed into a long sheet (see, for example, Japanese Patent No. 50-24466/1975).
The prior known sheet material cutting device of this type will be described below with reference to FIGS. 4 through 6. FIG. 4 a side view, FIG. 5 is a sectional plan view, and FIG. 6 is a plan view of a prior known sheet material cutting device.
In FIGS. 4 through 6, 51 is the main frame of the sheet material cutting device; 52 a screw shaft; and 51a a frame end. As shown in FIG. 5, one end of the screw shaft 52 is supported on the main frame 51 by means of a bushing 60 while the other end is supported on the frame end 51a by means of another bushing 60. The screw shaft 52 is fitted to said main frame by means of a screw 62 on one end and by a pulley 61 on the other. The pulley 61 is fitted to the screw shaft 52 by means of a stop ring 63. 53 is a supporting member which is fitted to said screw shaft 52 via a screw means. A rotary blade 54 is rotatably fitted to the supporting member 53 by means of a shaft 54a. A fixed blade 55 is fixed on said main frame 51 by means of a screw 56.
The pulley 61 is connected to a motor 57 via the transmission mechanism 58 shown in FIG. 6. In this particular device, the screw shaft 52 rotates via a transmission mechanism 58 and the pulley 61, as the motor 57 rotates. As the screw shaft 52 rotates, the supporting member 53, which is mounted on said screw shaft 52, travels along the screw shaft 52 horizontally between positions A and B in FIG. 5. As a result, a sheet material to be cut, which is fed vertically relative to the sheets of paper shown by FIGS. 5 and 6, is cut by the cooperation of the rotary blade 54 and the fixed blade 55 as the supporting member travels horizontally.
Since in the above-mentioned sheet material cutting device said screw shaft is supported by bushing 60 on both ends thereof without considering the elongation of the screw shaft 52 due to thermal expansion, the problem described below arises.
To design a more compact and lightweight sheet material cutting device, resins are increasingly used as materials for frames, screw shafts, etc. recently. For a sheet material cutting device using a lot of resins, different types of resins are generally used for the main frame 51 and the screw shaft 52 since these have a different functional purposes. Specifically, for example, glass fiber-reinforced resins with a relatively high rigidity are frequently used for main frames, while polyacetal resins or polypropylene resins with good sliding characteristics are frequently used for screw shafts that require sliding. For this reason, when a sheet material cutting device of this type is exposed to a high temperature (60.degree. C. or above), there occurs a difference of thermal expansion between the main frame 51 and the screw shaft 52 which are made of different materials. When said sheet material cutting device is transported on a ship, the temperature in the hold of the ship often reaches 60.degree. C. or above, with the result that the screw shaft elongates due to heat and deforms, preventing it from operating properly thereafter.
Furthermore, prior known sheet material cutting devices tend to cut thin and soft paper only bluntly as the blades wear out, or the paper is pushed back as the blades try to cut through and is eventually cut askew. In another case, the cutting plane of the paper may be fluffy or otherwise difficult to cut sharply.